Recycling of organic matter in Antarctic sediments: A transect through the polar front in the Southern Ocean (Indian Sector)

Christophe Rabouille,Jean‐Claude Relexans,Jean‐Francois Gaillard,Paul Tréguer,Marie‐Anne Vincendeau

doi:10.4319/lo.1998.43.3.0420

Abstract

Sediments from the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1. The first porewater distributions of O2 and NO3= and organic carbon data in the solid phase in this part of the ocean were used to model the recycling of organic matter in sediments. The data are described by a model containing two types of degradable organic matter with distinct reactivities. We estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average C : N ratio of 7. We estimate that particulate organic carbon fluxes deposited at the sediment‐water interface range between 0.2 and 0.8 mol C m−l y−l, with two peaks near the Polar Front and the Subantarctic Front. The flux 01 organic carbon deposited at the sediment‐water interface is unusually high and represents ˜10–20% of estimated primary production. From these findings, we conclude that production in the pelagic zone of this region is strongly linked to deposition and recycling in the sediment.

Highlights

Sedimentsfrom the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1
Assuming that early diagenesis is in steady state, we present a process model based on differential mass balances that allows estimation of benthic fluxes of POC, kinetics of POC decomposition, and C : N ratios of decomposing organic matter
Benthic-pelagic coupling in the AntarcticOur data and modeling work suggest that particulate organic matter deposited in the sediment of the Polar Front is composed of two different fractions with different reactivities

Summary

Introduction

Sedimentsfrom the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1. We estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average C :N ratio of 7. We estimatethat particulate organic carbon fluxes depositedat the sediment-water interface range between 0.2 and 0.8 mol C m--l y-l, with two peaks near the Polar Front and the Subantarctic Front. The flux 01 organic carbon depositedat the sediment-water interface is unusually high and represents-lo-20% of estimated primary production. The processes leading to recycling and burial of particulate organic matter in marine sediments affect the global oceanic carbon cycle over geological timescales. The recycling of organic matter in sediments is related primarily to mineralization reactivity and rain rate to the sea floor. Other key parameters include concentration of oxygen in overlying waters, bioturbation of surface sediment, and changes in sedimentation rate

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Conclusion